2.048 V shunt reference — the biasing resistor is the design decision
The LM4040BIM3X-2.0/NOPB is a precision 2.048 V shunt reference from TI's LM4040 family, housed in a three-pin SOT-23-3 package. It delivers a fixed 2.048 V output with ±0.2% initial tolerance and a 100 ppm/°C temperature coefficient — tight enough to set the full-scale voltage for a 12-bit ADC without external trimming. As a shunt reference, it behaves like a precision Zener: you bias it through an external resistor from the supply rail, and the part sinks current to maintain the regulated voltage. The cathode current must stay above 65 µA to keep the output in regulation; the maximum continuous cathode current is 15 mA.
Noise and drift — where the 35 µVrms matters
The 35 µVrms noise spec is integrated from 10 Hz to 10 kHz — that's about 17 ppm rms on a 2.048 V output. For a 12-bit ADC with a 4.096 V reference span, this noise contribution sits below 0.1 LSB, so you can skip the output filter cap in most designs. The 100 ppm/°C drift adds roughly 0.2 mV over a 0–70 °C swing, which is a ~0.01% shift — fine for industrial control loops but worth budgeting if you're chasing 16-bit accuracy without calibration.
Package and mounting — SOT-23-3 footprint
The part comes in a TO-236-3 / SC-59 / SOT-23-3 package — essentially the standard three-lead SOT-23 footprint.
Lifecycle and compliance — no end-of-life concern
The base product number is LM4040, which covers a range of voltage options and tolerance grades in the same SOT-23-3 footprint.